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M. J. Saeger, A. Fritz, L. Ptaszynski, H. Stoehr, R. Brinkmann, C. Klatt, F. Ruefer, J. Roider; Comparison of Optic and Optoacoustic Methods for Real Time Dosimetry in Selective Retina Treatment (SRT). Invest. Ophthalmol. Vis. Sci. 2009;50(13):223.
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© ARVO (1962-2015); The Authors (2016-present)
SRT is a laser method for selective treatment of the retinal pigment epithelium (RPE). The origin of RPE cell damage is related to laser induced microbubbles, forming around the intracellular melanosomes and thus disrupting the cell. This RPE damage is not visible in funduscopy. The desired RPE damage can be demarked by fluorescein angiography (FAG) after laser treatment. Therefore an experimental approach with three different methods for the detection of microbubbles in order to verify the treatment effect at the RPE was developed and evaluated.
931 laser spots were performed in 8 rabbit eyes. A frequency doubled Nd:YLF SRT-Laser was used: wavelength 527nm, pulse duration 1.7 µs, 30 pulses/spot, frequency 100Hz, spot diameter 200µm, energy range 50-400 µJ. Three dosimetry methods were employed to detect and document the treatment effect in the tissue: optoacoustic OA (making use of the pressure waves emitted by microbubble dynamics), optic interferometric OI (evaluating bubble wall velocity with probe light), and optic reflectometry RF (analyzing the change in reflected SRT laser power). The results obtained were correlated to a FAG score, performed after SRT: 1=not visible; 2=only visible in fluorescein angiography; 3=visible in ophthalmoscopy.
Altogether OA detected 56.12% (false positive 65.15%, correct positive 9%, false negative 3%, correct negative 25%), OI 54.86% (false positive 1%, correct positive 72%, false negative 22.72%, correct negative 3%) and OR 86.85% (false positive 11%, correct positive 67%, false negative 2.5%, correct negative 18.98%) of all applied spots.Correlated to FAG score1 0%, FAG score2 13.33% and FAG score3 50% of the spots were detected by OA; 26.67%, 22.22% and 50% by OI; 20%, 86.67% and 100% by OR.
In contrast to OA, the new dosimetry systems can detect bubble formation for every single pulse in real time. However, all three methods for microbubble formation due to SRT treatment are giving an immediate feedback and seem to be useful for an online dosimetry control. OA and OI show a reduced accuracy of measurement caused by the anatomy of rabbit eyes. Currently the new dosimetry systems are also performed on human eyes, results remain to be evaluated. Thus the FAG as diagnostic procedure will probably be dispensable in future.
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